Open-culture biotechnological process for triacylglycerides and polyhydroxyalkanoates recovery from industrial waste fish oil under saline conditions

Industrial waste fish oil streams contain high concentrations of medium and long-chain fatty acids suitable to produce value-added compounds. However, to process them dilution is required, and the water produced in the fish-canning industry commonly contains high salinity, which might limit its reuse as a dilution stream. Although NaCl is well-known to negatively affect biological activity, its effect on triacylglycerides (TAG) and polyhydroxyalkanoates (PHA) storage has not been well studied yet. Here, it was explored if intracellular TAG and PHA production can be efficient under saline conditions (10 g NaCl/L). For that purpose, waste fish oil was valorised using a mixed microbial culture (MMC) in a two-stage process (culture selection plus accumulation). Results showed that salinity influenced not only the activity but the structure of the microbial communities developed in the bioreactors. The bacterial genera Acinetobacter and Rhizobium and the mold Candida glaebosa clade were observed as the storing microorganisms which abundance increased under saline conditions whereas Dipodascus and Mortierella notably decreased. Nonetheless, despite the osmotic stress, promising results were obtained and maximum intracellular accumulations of 54.2 wt% (TAG:PHA = 28:72, 0.131 Cmmol_TAG/Cmmol_S, 0.303 Cmmol_PHA/Cmmol_S) and 50.9 wt% (TAG:PHA = 63:37, 0.291 Cmmol_TAG/Cmmol_S, 0.114 Cmmol_PHA/Cmmol_S) were observed when PHA and TAG were preferentially stored, respectively.